Surface wave generator



Jan 16, 1962 b. l.. couRsEN A 3,016,831

SURFACE WAVE GENERATOR Filed 00t- 2. 1958 Elg- 1 4 Sheets-Sheet 1 PFIPFZ Pr PF4 PF5 Pf6 PF7 Pra INVENTOR DAV/D I /NN coURsEN ATTORNEY Jan.16, 1962 Filed 001,. 2. 1958 Eig.

D. L. COURSEN SURFACE WAVE GENERATOR 4 Sheets-Sheet 2 ifi .l 35 f 2,

'.iiiill .n.mmllrlylllll' -INVENTOR DAVID LINN COURSEN "www L ATTORNEYJan. 16, 1962 D. l.. coURsEN SURFACE WAVE GENERATOR 4 Sheets-Sheet 3Filed Oct. 2, 1958 DA VID LINN COURSEN BY @a ATTORNEY Jan. 16, 1962 DCQURSEN 3,016,831

SURFACE WAVE GENERATOR Filed 001'.. 2, 1958 4 Sheets-Sheet 4 INVENTOR.DAVID LINN COURSEN ATTORNEY 3,016,831 SURFACE WAVE GENERATOR David L.Coursen, Newark, Del., assignor to E. I. du Pont de Nemours andCompany,Wilmington, Del., a corporation of Delaware Fiied Oct. 2, 1958, Ser. No.764,916 3 Claims. (Cl. 102-22) The present invention relates to a novelhigh-explosive device wherein the natural detonation front is distorted.More particularly, the present invention relates to a surface-wavegenerator, i.e., a high-explosive device wherein a detonation frontgenerated at one point is made to arrive simultaneously at a pluralityof points on a desired surface.

When a homogeneous mass of a high explosive in initiated at one point,the resultant detonation front proceeds outwardly from the point ofinitiation at uniform velocity in all directions. For example, in thecase in which a spherical charge of a high explosive is initiated at itscenter, the detonation front travels uniformly through the charge as anexpanding sphere, the front eventually arriving simultaneously `at allpoints on the surface of the charge. When, however, the spherical chargeis not initiated at its center but at an eccentric point such as a pointnear its surface, the detonation front in this second case initiallyconstitutes an expanding sphere until the portion of the boundarynearest the point of initiation is reached. Thereafter, the fronttravels through the remainder of the charge as an expanding segment of asphere, the radius of curvature of the segment at any given point in thecharge being determined by the distance from the initiation point. Inthe third case, a non-spherical homogeneous mass of explosive, e.g. apyramid, centrally or eccentrically initiated, the detonation frontproceeds in the same manner as in the eccentrically initiated sphericalcharge. It is obvious that in either case 2 or case 3 the detonationfront, because of its natural curvature, does not arrive simultane ouslyat all points on the surface of the charge but arrives at various timesdepending upon the distance between each finish point and the starting,or initiation, point.

In many applications of explosives besides blasting, it is desirable toemploy an explosive charge wherein the detonation front arrivessimultaneously at a plurality of predetermined points on one or moresurfaces of the charge. For example, U.S. Patent 2,604,042 (Cook, I. H.,-to Imperial Chemical Industries, Ltd., July 22, 1952) describes amethod whereby a metal surface is embossed by means of a planedetonation front, i.e. a d-etonation front which is distorted to arrivesimultaneously at a plurality of points on a surface. The explosivecharge used is a composite charge consisting of several diiferentexplosives, each having a different detonation velocity. The form of thecharge is such that not only a great deal of care must b taken incorrelating the different detonation velocities but also a largequantity of explosive material must be incorporated into the charge.This large amount of explosives increases the cost of the unit and,moreover, frequently results in the destruction of the adjacent metalsurface due to the brisance of the explosive which is present in suchlarge quantities. Obviously, the provision of a charge: capable ofproducing the desired distortion of the detona-v tion front and yetconsisting of an inherently smaller quantity of explosive material is ofgreat value in this application. Moreover, the use o-f such asurface-wave generator is exceedingly Valuable in basic investigationsof explosive phenomena. For example, in a fundamental study of thesubjection of objects such as metal plates to Patented .iai-n. i6, i962explosive superpressures, i.e. the exceedingly high pressures of shortduration generated by a high explosive, a determination of the effect ofa plane detonation front is of interest. A prerequisite of such aninvestigation of course is the availability of an explosive charge whichnot only will generate the plane detonation front but also not destroythe object subjected to the superpressures.

Accordingly, an object of the present invention is the provision of anexplosive device whrerein the detonation front generated at one point isdirected to arrive simultaneously at a plurality of points on a surface.Another object of the present invention is the provision of asurface-wave generator in which only one explosive composition isrequired. A still further object of the present invention is theprovision of a surface-wave generator causing a minimum of damage toadjacent objects.

I have found that the foregoing objects may be achieved when l provide asurface-wave generator comprising a plurality of layers of acap-sensitive high-explosive in conormal relationship, the thickness ofeach of the explosive layers being such as to exceed the minimumthickness for support of the detonation, each of the explosive layersbeing separated one from another by a barrier plate provided with anarray of detonationtransmitting channels, th-e array of the channels insuccessive plates being such that the axis of each channel in a givenplate is equidistant from the axis of each of a plurality of channels inthe immediately following plate. In accordance with the presentinvention, the thickness, lz, of a given barrier plate and thethickness, z of the explosive layer superincumbent upon the givenbarrier plate are so interrelated with the wall-to-wall lateraldisplacement, a, of the base of a channel in the channel in the givenbarrier plate and the base of the nearest channel in the immediatelypreceding plate that ythe ratio of the lateral displacement, a, to thebarrierplate thickness, h, is at most inner In order to describe morecompletely the nature of the present invention, reference now is made tothe accompanying drawings, in which:

FIGURE l is a front View in cross-section of a surface-wave generatorconstructed in accordance with the principles of the present invention,the unit being depicted in a manner such as to facilitate anunderstanding of the theoretical considerations involved in theinvention,

FIGURES 27 represent various embodiments of the unit of the presentinvention, and

FIGURE 3b is a section taken along line Sly-3b of FIGURE 3.

Referring now to the figures, especially to FIGURE 1, in more detail, inall drawings, P0 is the starting, or initiation, point; E is theexplosive layer; B is the barrier plate; C is thedetonation-transmitting channel in barrier plate B; and PF is a finishpoint on the surface of the unit.

The explosive uni-ts of the present application are based upon thefollowing principles: (l) a homogeneous explosive mass normallydetonates at uniform velocity in all directions and (2) the detonationgenerates in adjacent nonexplosive materials a shock which propagatesthrough the material at a velocity which may be distinct from that ofthe detonation velocity and is capable of initiating detonation in anadjacent mass of explosive. Considering rst a solid homogeneousexplosive block of the form shown in FIGURE l, the detonation frontinitiated at point P0 and moving at uniform velocity will proceedthrough the block in the main as an expanding segment of a sphere. Thus,the front will arrive first at the finish points, PF4 and PF5, which arenearest to initiation point P and last at the furthest points PF1 andPFS Now, if layers of a material in which the shock velocity is equal tothe detonation velocity of the explosive are interposed between layersof explosive, i.e. if the barrier plates B of FIGURE 1 were composed ofsuch a material, the time interval required for the shock to travelthrough a plate of this material would equal the time required for adetonation front to travel an equivalent distance through explosive.Thus, in this case the detonation front would again arrive at PF4 andPF5 first and PF1 and PFB last.

In the case in which the barrier plates B comprise a material having ashock velocity lower than the detonation velocity of the explosive, thetime interval required for the shock to travel through a plate of thismaterial would exceed that time required for the detonation to travel anequivalent distance through explosive. Thus, considering two layers ofexplosive separated by a plate of low shock velocity material, the timeinterval between the initiation of the detonation in the upper mostlayer and the completion of the detonation process in lowermost layerwould be greater than that resulting when the two layers are separatedby an explosive layer equal in thickness to the barrier plate.

Now, if channels C are provided in the low shock velocity barrier platesB, through which channels the detonation-propagating stimulus istransmitted at a rate higher than the velocity of theinitiation-inducing shock traveling through the plate, those portions ofthe explosive layer below the channels will be initiated first and therest of the layer later or not at all if the shock has decayed to thelevel at which itis incapable of effecting initiation. I have found thatby alternating explosive layers and barrier plates having a shockvelocity lower than the detonation velocity and provided withdetonation-transmitting channels in the proper array, an explosive unitmay be constructed in which the natural detonation front is distorted toarrive simultaneously at a plurality of points on its base. The channelsare such that the Vertical component of the Velocity of the agent whichtransmits the detonation therethrough exceeds the velocity of the shockpassing through the remainder of the barrier plate. Thus,

the detonation-transmitting channels C in barrier plate B may be filledwith an explosive E, as is shown in FIGURE 3b, or they may be airfilled, the detonation passing over air gaps of proper size withoutdying out and more rapidly than the shock proceeds through the barriermaterial. The channels in the plates define a plurality of paths betweenthe starting point, P0, and the finish points, PF, along which thedetonation-transmitting stimulus travels at a uniform rate higher thanthat of the shock passing through the barrier plates. Although amultiplicity of paths exist, for every finish point there is a shortestpath from the starting point. To effect the desired simultaneous arrivalof the detonation front at a plurality of finish points, the timerequired for the detonation front to travel through all the shorteststarting point-finish point paths defined by the channels must be equal.Thus, since the detonation is traveling at uniform rate along all thepaths, all shortest paths must be equal in length. To provide theequilength shortest paths, the channels are so arrayed in successiveplates that the axis of each channel in a given barrier plate isequidistant from the axis of each of a plurality of channels in theimmediately following plate.

FIGURE 2 illustrates one unit constructed in accordance with theaforespeciied requirements. In this unit, two channels C are provided inthe uppermost barrier plate B and the channels in the next plate aredisposed in square array below the upper channels. In this unit asshown, the detonation front travels through 42 channels in the lowermostplate and thus arrives simultaneously at 42 finish points on the base ofthe unit. A mathematical expression, Equation l, may be set up relatingthe number of channels C in a given plate B for this unit:

M being the number of channels and N being the barrier plate number.

FIGURE 3 shows another embodiment of the surfacewave generator of thepresent invention. In the depicted units of this embodiment, the frontarrives simultaneously at 36 nish points on the base. The unit shown hasive barrier plates and 4 channels in the upermost plate, the equationrelating the number of channels in a plate to the plate number being:

In FIGURE 4 showing another embodiment of the present invention, the topplate of the unit again is provided with four channels, the number ofchannels in a given plate being related to the plate number inaccordance with Equation 3:

M :22N (Equation 3) A unit such as this having 4 barrier plates providesfor simultaneous initiation at 256 points on its base.

The unit of. FIGURE 5 is a slight modification of that shown in FIGURE4, the four channels in the uppermost plate being formed by cutting awaythe corners of the plate. In the lower plates, the channels are formedby cutting away the four corners of each plate and also cutting away, asshown, portions along the edges of the plate, which portions are definedby adjacent pairs of channels of the FIGURE 4 embodiment. Channels areprovided symmetrically in the interior portions of the lower plates,which portions correspond to squares delineated in the plate by theFIGURE 4 channels. Each concave corner of the `cut-away portions acts asa detonation-transmitting channel. In the plates in' the FIGURE 5embodiment, Equation 3 also governs the relationship between number ofchannels in a given plate and plate number.

In FIGURE 6 is shown a series of hexagonal barrier plates, B1-B4,suitable for use in another embodiment of the instant surface-wavegenerator, only the plan view of the plates being shown for simplicity.The uppermost plate is provided with six channels in hexagonal array,the flats of all hexagons delineated by the channels in the plates beingparallel to an edge of the plate. The relation governing the number ofchannels in a given plate with respect to plate number is set forth inEquation 4:

Inasmuch as the fourth, and last, barrier plate shown for the FIGURE 6embodiment has 552 channels, the total number of finish points at whichthe detonation front arrives simultaneously equals 552.

Again for simplicitys sake, the circular barrier plates of the FIGURE 7embodiment rather than the complete unit are represented. In thisembodiment as shown, ve plates-are used. In B1, the uppermost of thebarrier plates, 6 channels are provided in hexagonal array. The channelsin the subsequent plates are also in hexagonal array, the channels in'the subsequent plates being so positioned that the hexagons thusdelineated' are rotated 30/on their axes with respect to the hexagons inthe previous plate. The mathematical expression relating the number ofchannels in a given plate to the plate number is:

N being greater than l and M equalling 6 when N equals 1. Since B5, thelowermost barrier plate shown, thus contains 876 channels, there. willbe 876 simultaneous finish points in the units as constructed.

Regardless of the exact configuration of the surfacewave generator ofthe present invention, several basic requirements must be fullled inorder that the detonation front will arrive simultaneously at a numberof finish points on its base. First, the unit must be constructed ofconormal layers of a cap-sensitive high explosive alternated withbarrier plates, and the explosive layers must be of sufficient thicknessfor support of the detonation. The barrier plates must be provided withan array of detonation-transmitting channels which are so disposed insuccessive plates that the axis of each channel in a given plate isequidistant from the axis of each of a plurality of channels in theimmediately following plate. Lastly, referring again to FIGURE 1, thethickness, h, of a given barrier plate and the thickness, z, of anexplosive layer superincumbent upon the given plate must be sointerrelated with the wall-to-wall lateral displacement, a, of the baseof a channel in the given barrier plate and the base of the nearestchannel in the immediately preceding plate that the ratio of the lateraldisplacement, a, to the barrierplate thickness, h, is at most naar Theexact cap-sensitive high explosive used in the units of the presentinvention is not critical. Suitable explosives include such crystallinecompounds as RDX, HMX cyclotetramethylenetetranitramine), PETN, leadazide, nitromannite, and the like, which may be prepackaged in layerlikethin-walled containers for incorporation in the unit. However, for easelof handling and ease of thickness control, the use of self-supporting,coherent, sheet-like explosive layers is preferred. Such self-supportinglayers may be formed by admixing one of the afore-named crystallinecompounds with a suitable binding agent, or such gelatinous masses asblasting gelatin formed from nitroglycerin, which normally is a liquid,may be used, Preparation o-f the units at times may be facilitated byuse of those binary castable mixtures such as cyclotol (a TNT-RDXmixture), pentolite (a TNT-PETN mixture), and tetrytol (a tetryl-TNTmixture).

The thickness of the explosive layer must exceed the minimum thicknessrequired for support of detonation. Since the minimum thickness isdependent upon the specific explosive used, no exact value may bespecified for the required minimum thickness of the explosive layer.However, I have found that for a very sensitive explosive the minimumthickness for support of the detonation is 0.2 millimeter. Therefore, ona practical basis, the lower limit on explosive layer thickness may bestated to be at least 0.2 millimeter.

The specific material used as the barrier plate is not critical, so longas its shock velocity is lower than the detonation velocity of thespecific explosive used. For example, steel having a shock velocity of5000 meters per second would be unsuitable when the explosive detonatesat a velocity of 3000 meters per second but would be suitable with anexplosive detonating at a rate of 6000-7000 meters per second. Suitablebarrier materials include cardboard, felt, cork, wood, foamed aluminum,among many others. Because of their low shock velocity, such substancesas foamed aluminum are preferred. However, various other factorsincluding economics, availability, ease of handling, and the like willalso be considered in the selection of the exact barrier plate materialused.

In order to effect the desired functioning of the units, the barrierplates must be provided with detonation-transmitting channels in properarray as aforedelined. These channels may be disposed at right angles tothe horizontal surface of the barrier plate or they may be disposed atoblique angles to this surface. The detonation is transmitted throughthese channels at a rate greater than that at which the shock istransmitted through the barrier plate itself. Thus. the channels maymerely constitute air gaps between adjacent layers of explosive or theymay he filled with explosive and thus constitute explosive trainsbetween adjacent layers of explosive. When airflled channels are used, alayer of thin metal foil, eg. of lead, may be inserted between theexplosive layer and the barrier plate, the foil, which produces metalparticles, acting to enhance propagation across the air gap.

Regardless of whether the channels constitute air gaps or explosivetrains, the cross-sectional area of the channel must be at least 0.04square millimeter. When the channels are explosive filled, theirlengthis immaterial. On the other hand, when the channels constitute air gaps,their maximum length should not exceed that'distance across which thedetonation is sustained. Inasmuch as this maximum distance is a directfunction of the specific explosive used, no exact value may be set forthe maximum length of air gap. In correlation with this consideration,the thickness of the barrier plate also is a factor, since the thicknessis directly related to the channel length. The barrier plate thickness,h, as afore-indicated, is interrelated with both the thickness of theexplosive layer, z, and the previously defined lateral displacement ofchannels in adjacent layers in accordance with the equation:

Thus, the thickness of the barrier is governed not only by the thicknessof the explosive layer but also the extent of the lateral displacementof channels. Therefore, no exact value can-be set for the barrierthickness. As has been indicated, however, the length of the air-filledchannels must not exceed that distance across which the detonation issustained. Thus, in the case of this type of channel the thickness ofthe barrier plate must not exceed that value which will provide for themaximum length air gap, whether the channels be at right or obliqueangles to the surface of the barrier plate. Naturally, there is nolimitation on the maximum barrier thickness when the channels are filledwith explosive aside from that dictated by the previous equation.vHowever, inasmuch as the use of excessively thick barriers generallyserves no useful purpose while increasing the over-all cost and size ofthe unit, the limitation on maximum barrier thickness imposed by the useof air gaps will serve for all practical purposes when theexplosive-filled channels are used.

In this connection, it must be stated that definite principles serve todetermine the mathematical expression derived to interrelate thickness,z, of the explosive layer, which thickness on a practical basis willalways be at least 0.2 millimeter, thickness, h, of the barrier platebelow the given explosive layer, and the positioning of the channels inthis plate as defined by a, the wall-to-wall lateral displacement of thebase of a channel in this plate and the base of the nearest channel inthe immediately preceding plate. Referring again to FIGURE 1 andassuming the limiting case that the time required for the shock totravel directly through the barrier along R1 equals the time requiredfor the detonation to travel along the longer path, R9, defined by thedetonation-transmitting channel, the following expression may be set up:

wherein Z, h, and a are as aforedefined and illustrated in FIGURE l, Dis the detonation velocity of the explosive, and S is the shock velocityin the barrier. This expression may be rearranged to give the condition:

*Utrera-rar the ratio decreasing with less dense and porous materialsand lower velocity explosive. Consequently,

tatu-2er this feature being dependent vupon the application to which theunit will be put. A unit constructed in accordance with the requirementsof the invention may be so built to provide only a few, widely spacedfinish points on 5 a given surface area by spacing the channels farapart.

In the addition to the six exemplified configurations of By usingclosely spaced channels, the number of finish the surface-wave generatorof the present invention, many points on a given `area may be greatlyincreased. As other configurations and/ or variations on the exemplifiedafore-stated, the height of the unit is regulated in the main units maybe constructed in acco-rdance With the previouS- by the number of platesemployed. The bottom surface ly specified requirements. The exactconfiguration used m of the unit may consist of an explosive layer or abarrier will be selected on the basis of the application to which itplate depending upon the application to which the unit is is put, suchfactors as the number of finish points desired put. Furthermore, the useof a one-channel barrier plate on the base of the unit, the over-alldimensions of the unit, as the uppermost surface is also very feasible,the channel economics, and the like. As has been shown, the numberacting, in part, as a supporting means for the initiator, for of finishpoints varies with the particular configuration used example an electricblasting cap, or the cap may be and with the number of barrier platesdisposed in the given configuration. The following table serves toillustrate these points.

abutted against an uppermost explosive layer.

As has been indicated, a number of methods are feasible for thepreparation of the units, the exact explosive Table Figure 2 Unit Figure3 Unit Figure 4 Unit Figure 5 Unit Figure 6 Unit Figure 7 Unit (19111)*(E 12)1 (Eq 3)* (Eq- 3)* (Eq. 4)* (Eq- 5)* Barrier Plate No.

No. of No. of No. of No. of No. of No. of No. of No. of No. ot No. ofNo. of No. of Chan- Finish Chan- Finish Chan- Finish Chan- Finish Chan-Finish Chan- Finish nels Pts'. nels Pts. nels Pts. nels Pts. nels Pts.nels Pts.

2 2 4 4 4` 4 4 4 e 6 s s 6 v6 9 9 16 16 16 16 30 30 24 24 12 12 16 16'64 64 64 64 132 132 ,84' 84 20 25 25 256 256 256 256 552 552 276 276 3036 36 1, 024 1.024 1. 024 1.024 2, 256 2, 256 876 876 42 42 49 49 4, 0964, 096 4, 096 4, 096 9, 120 9, 120 2, 724 2, 724

1 Equation numbers refer to the previously specified equations relatingthe number of channels in a given plate to the plate number in a givenembodiment.

As clearly shown in this table, certain embodiments of the usedgenerally dictating the preparative procedure. If

surface-wave generator of the present invention, for example the FIGURES2 and 3 units, inherently give fewer finish points per given platenumber than do others, for example, the FIGURE 6 unit, Moreover, thenumber of finish points in a given unit increases with increase in thenumber of plates employed in the unit. If the application in which theunit is to be used requires the latter to provide only a few finishpoints, e.g. l2, a FIGURE 2 unit constructed to contain only 3 plateswould be suitable. On the other hand, when a very great number of finishpoints are required for the application, the FIGURE 6 unit having 6 ormore plates would be used.

In general, the units will be so designed that the initial barrier platecontains more than one channel. When one channel is used in theuppermost plate, it acts solely as an initiation point. At times, suchconstruction, however, may be desirable. Usually, also, at least twoplates will be provided in each unit, one plate seldom providingsufficient finish points for the application and the use of at least twoplates insuring the proper timing of the unit.

Although for ease of description due to simplicity, only those unitshaving explosive layers and barrier plates which are coplanar have beenillustrated, the invention is not restricted to units having suchcoplanar elements, the only requirement being that the explosive layersand barrier plates be disposed in conormal relationship. Thus, forexample, a unit may be constructed in which the explosive layers andbarrier plates constitute segments of a sphere disposed in conormalrelationship. In the resulting unit, the finish points, naturally, willbe on a curved rather than planar surface. A number of such segmentalunits may be assembled to provide a spherical unit giving a plurality offinish points on the interior surface of the sphere. Of course, a numberof any of the exemplified configurations may also be assembled. Thisprocedure may be used, for example, when the number of finish pointsdesired is large but a unit limited in height is needed, the increase inplates required to increase the number of finish points in a given unitobviously increasing also the height of the unit.

The over-all dimensions of the unit are not cri-tical,

use of a castablc explosive is desired in a unit having explosive-filledchannels, the barrier plates provided with channels in the proper arraymay be supported at the desired spacing within a mold and heated, andthen the explosive melt will be poured into the mold. After cooling, theunit is removed from the mold. The explosive melt may also be cast intofiat slabs, which are then alternated with the barrier plates, forexample if the use of air gaps for the detonation-transmitting channelsis desired. When the self-supporting layers of explosive are used, theyare merely alternated with the barrier plates, the channels being filledwith explosive or not as desired. Although for ease of manufacture itmay be desirable to use only one explosive composition in the unit,several different compositions may also be employed if the obtaining ofspecial results is required. For example, the lowermost layer maycomprise a more highly brisant explosive than the explosive of theprevious layers. The explosive in a given layer, however, must detonateat uniform velocity.

The invention has been described in detail in the foregoing. However, itwill be apparent to those skilled in the art that many variations arepossible without departure from the scope of the invention. I intend,therefore, to be limited only by the followingclaims.

I claim:

l. A surface-wave generator wherein the natural detonation front isdistorted to arrive simultaneously at a plurality of points on itssurface which comprises a plurality of parallel layers of cap-sensitive,high explosive in conormal relationship to one another, the thickness ofeach of said explosives being at least 0.2 mm. and such as to exceed theminimum thickness for support of the detonation, each of said explosivelayers being separated one from another by a barrier plate provided withan array of detonation-transmitting channels, the barrier plate being ofa material having a shock velocity lower than the detonation velocity ofthe explosive, the array of said channels in successive plates beingsuch that the axis of each channel in a given plate is equidistant fromReferences Cited in the file of this patent UNITED STATES PATENTS JasseFeb. 17, 1953 MacLeod Dec. 18, 1956 Moses Oct. 15, 1957 FOREIGN PATENTSGreat Britain May 12, 1954

